1. Field of the Invention
This invention generally relates to a light-to-light conversion element and an imaging device and more particularly to a light-to-light conversion element suitable for a high resolution image displaying device or imaging device, which stores information represented by an electromagnetic wave signal such as light by making electric charge correspond to the information and then reads the information as an electromagnetic wave signal, and to an imaging device using such a light-to-light element.
2. Description of The Related Art
Referring first to FIG. 8, there is shown an example of a light-to-light conversion device of the related art, in which information represented by an electromagnetic wave signal such as light by generating electric charge corresponding to the information is stored and then the information is read by using an electromagnetic wave signal such as light. This example is disclosed in Japanese Patent Application filed on May 16, 1989, by Applicant of the instant application.
As shown in this figure, this light-to-light conversion device includes a surface conversion element 10 and a light-to-light conversion element 12. Further, as indicated by an arrow F1, electro-magnetic flux signals representing various information including time series information are scanned and are then incident on the surface conversion element 10 whereon the times series information is recorded and then converted into surface information. Subsequently, the surface information on each recorded surface of the element 10 is outputted to the light-to-light conversion element 12 as indicated by an arrow F2.
From the light-to-light conversion element 12, the surface information recorded on each surface of the element 10 and inputted thereto is read by using read light inputted thereto as indicated by an arrow F3. Thus, the light incident on the light-to-light conversion device as indicated by the arrow F1 is converted into another light indicated by an arrow F4 and is outputted therefrom. Thereby, the time series information is converted into the surface information.
The read light indicated by the arrow F4 is projected onto a screen (not shown) and then a corresponding image is displayed thereon.
However, in the light-to-light conversion device of the related art as above described, the reflection of the read light is not always favorably performed. For instance, the device of the related art has a defect that even when light having wavelength different from wavelength of the read light is incident thereon, the reflection of such light is effected and thus a high contrast cannot be obtained. The present invention is accomplished to eliminate such a defect of the related art.
Therefore, it is an object of the present invention to provide a light-to-light conversion element which can give a high contrast to an image obtained from image information such as color information.
Incidentally, as examples of application of a conventional wavelength conversion element or device for converting an invisible electro-magnetic radiation beam such as light to a visible electro-magnetic radiation beam, there can be cited a device disclosed in the specification of the U. K. patent No. 663339 in which an X-ray image is displayed on a television monitoring receiver by using a wavelength conversion device, and also can be cited a well known noctovision. However, such a wavelength conversion element or device has drawbacks that the construction thereof is complex and that it is difficult to obtain a high definition visible image. The present invention is accomplished to eliminate such drawbacks of the conventional element or device.
Therefore, it is another object of the present invention to provide a light-to-light conversion element or device which has simple construction and can obtain a high definition visible image.
Further, as examples of a light-to-light conversion element of the related art constructed in such a manner to input an optical image and output an optical image, can be cited microchannel spatial light modulators such as a liquid crystal type photo-modulation device, photoconductive Pockels effect element and a microchannel type photo-modulation device and elements made from photocromics material. Such light-to-light elements have been noticed as elements for use in a photo-writing projector, an optical computer and so on. Further, the assignee of the instant application has proposed a high resolution imaging device using a light-to-light conversion element.
FIG. 14 is a schematic sectional side view of a light-to-light conversion element of the related art, which is proposed to eliminate the drawbacks of the conventional element or device as described immediately above (More detailed practical construction of the light-to-light conversion element of the present invention accomplished to eliminate the drawbacks of the conventional element or device as described immediately above will be explained later). In this figure, reference numerals 201 and 202 denote glass-plates; 203 and 204 transparent electrodes; 205, 206 and 211 terminals; 207 a photoconductive material layer member; 208 a dielectric mirror; 209 an optical member (for example, photo-modulation material such as a single crystal of lithium niobate or a nematic liquid crystal) capable of changing the state of light correspondingly to the field strength of the applied power source; WL a write light; RL a read light; and EL light for erasure of electric charges generated in the light-to-light conversion device PPC.
In FIG. 14, the direction of the light (hereunder sometimes referred to as erasure light) EL for the erasure of the generated electric charges is shown as the same as that of the read light RL. This shows the direction of the incidence of the light for the erasure on the conversion element in case where the dielectric mirror 208 having a light transmission characteristic as shown in FIG. 15 is used. Incidentally, it is apparent that the direction of the incidence of the light used for the erasure of the charge image is same as that of the incidence of write light in case of the conversion elements constructed such that the light used for the erasure of the charge image is incident thereon in the same direction as that of the incidence of write light.
Further, when optical information is written into the conversion element of FIG. 14, a circuit consisting of a power source 210 and a switch SW is connected to the terminals 205 and 206 of the light-to-light conversion element. Further, a movable contact of the switch SW is placed in the position of a fixed contact WR in accordance with a switch control signal supplied at an input terminal 211 of the switch SW. Then, a voltage from the power source 210 is applied across the transparent electrodes 203 and 204 such that an electric field be applied across the photoconductive material layer 207. Hereupon, a write operation of writing the optical information into the conversion element is performed by making write light beam WL be incident on the glass-plate 201 of the conversion element.
Namely, the write light WL, which has been incident on the conversion element as above described, passes through the glass-plate 201 and the transparent electrode 203 and reaches the photoconductive layer material member 207. At that time, the electric resistance of the photoconductive material layer member 207 changes correspondingly to an optical image formed by the incident light WL having reached thereto, so that electric charges corresponding to the optical image formed by the incident light having reached thereto are generated on the boundary surface between the photoconductive material layer member 207 and the dielectric mirror 208.
The reproduction of the optical information written into the conversion element in the form of the charge image corresponding to the optical image formed by the incident light is performed by projecting read light RL having constant intensity onto the glass-plate 202 from a light source (not shown) under conditions that the movable contact of the switch SW is placed in the position of the fixed contact WR thereof and the voltage from the power source 210 is applied across the transparent electrodes 201 and 202.
As above described, the charge image corresponding to the optical image formed by the incident light reached thereto is generated on the boundary surface between the photoconductive material layer member 207 and the dielectric mirror 208 of the conversion element into which the optical information is written by using the incident light, so that an electric field having strength distribution corresponding to the optical image is applied to the photo-modulation material layer member 209 (for example, the single crystal of lithium niobate 209) which is connected in series to the photoconductive material layer member 207 along with the dielectric mirror 208.
Further, the refractive index of the single crystal of lithium niobate 209 changes due to electrooptic effects correspondingly to an electric field. Therefore, when the electric field having strength distribution corresponding to the charge image is applied to the single crystal of lithium niobate 209 which is connected in series to the photoconductive material layer member 207 along with the dielectric mirror 208, the refractive index of the single crystal of lithium niobate 209 changes in accordance with the charge image corresponding to the optical image formed by the incident light reached thereto.
Moreover, when the read light RL is projected on the glass-plate 202, the read light RL projected on the glass-plate 202 propagates through the transparent electrode 204, the single crystal of lithium niobate 209 and the dielectric mirror 208 in this order. Subsequently, the read light RL is reflected by the dielectric mirror 208 and then returns to the glass-plate 202 as reflected light. However, as above described, the refractive index of the single crystal of lithium niobate 209 changes due to the electrooptic effects correspondingly to the electric field. Thus, the reflected read light RL comes to include information corresponding to the strength distribution of an electric field applied to the single crystal of lithium niobate 209 by the electrooptic effects of the single crystal of lithium niobate 209 and further forms a reproduced optical image corresponding to the optical image, which is formed by the incident light on the glass-plate 202.
As is apparent from the foregoing description, the dielectric mirror 208 of the conversion element reflects the read light RL, which has been incident on the photo-modulation material layer member 209 from the side of the transparent electrode 204, thereby preventing the read light from transmitting through the photo-modulation material layer member 209 and the photoconductive material layer member 207.
Further, can be prevented the occurrence of a problem to be resulted from the transmission of the read light RL through the photo-modulation material layer member 209 and the photoconductive material layer member 207, that is, a problem that the charge image is disturbed by transmitting through the photo-modulation material layer member 209 and the photoconductive material layer member 207. Incidentally, in a related art light-to-light conversion element, a light insulating film is provided in place of a dielectric mirror.
Thus, light which is incident on the photoconductive layer and the photo-modulation layer is selectively reflected by the reflection layer. Thereby, a writing of and a reading of information can be selectively effected in response only to light of specific wavelength. Moreover, information having a high contrast ratio can be obtained without degrading a resolution.
Furthermore, erasure of the information written by using the write light is effected by supplying a switch control signal to the input terminal 211 of the switch SW to place the movable contact of the switch SW in the fixed contact E thereof, then equalizing electric potentials of the terminals 205 and 206 of the conversion element in such a manner to prevent the generation of an electric field and further making the erasure light EL having uniform strength distribution be incident on the glass-plate 201, on which the write light WL has been incident. Further, in case where the characteristic of transmittance of light through the dielectric mirror 208 with respect to wavelength of light is just as shown in FIG. 15 with reference to the read and write light RL and EL, the erasure of the information written by using the write light is effected by making the erasure light EL having uniform strength distribution be incident on the glass-plate 202 as shown in FIG. 14.
As above described, in this light-to-light conversion element of the related art, a dielectric mirror (or a light insulating film) is provided between the photo-modulation material layer member 209 and the photo-conductive material layer member 207 in order to prevent the charge image from being disturbed by transmitting through the photo-modulation material layer member 209 and the photo-conductive material layer member 207. However, in case where a dielectric mirror (or a light insulating film) is provided between the photo-modulation material layer member 209 and the photo-conductive material layer member 207, the electric field occurring due to the charge image on the boundary surface between and the photo-conductive material layer member 207 and the dielectric mirror 208 is expanded by the presence of the dielectric mirror (or the light insulating film) having film thickness and such an expanded electric field is applied to the photo-modulation material layer member 209. Further, the electric field occurring due to the charge image on the boundary surface between the photo-modulation material layer member 209 and the photo-conductive material layer member 207 is also expanded by the fact that impedance of the dielectric mirror 208 (or the light insulating film) is finite. As a result, resolution of the device is decreased. The present invention is accomplished to resolve such a problem of the device of the related art.
Accordingly, it is still another object of the present invention to provide a light-to-light conversion device wherein the dielectric mirror, which is an important factor of deterioration in resolution and of reduction in contrast, is omitted and further the photoconductive material layer member is directly piled on the photo-modulation material layer member.